This is from the third letter MT ever wrote to Olivia L. Langon, of which only this postscript survives. Harriet Elinor Smith and Richard Bucci, who edited the letter for the Mark Twain Project, date it 4-5 October 1868, and speculate that the other pages of this letter may be missing because in them MT violated the conditions Livy had set for their correspondence: i.e. that he write to her as a brother, not a suitor. If so, perhaps the unusual signature is meant to suggest that it was "Mark" who broke the rules and transgressed that way, not "Samuel," her "affectionate brother."
This page appears here with permission of the Mark Twain Papers, UC Berkeley. To see the letter as annotated by the Project, use the link below right, and search for MS: CU-MARK, UCCL 02770.TRANSCRIPT OF THIS PAGE | MARK TWAIN PROJECT